This invention relates to a method of filling a borehole with grout capsules, as well as to a grout capsule gun.
Conventional grout capsule guns are generally used to fire grout capsules into a borehole, so as to fill the borehole prior to or after the insertion of a support member, such as a rockbolt, into the hanging wall of a mine tunnel, for instance. While such grout capsule guns have been found to perform relatively well in respect of shorter boreholes, it has been found that those boreholes having a greater depth are not always completely and uniformly filled with grout capsules. Non-destructive testing of holes which have not been uniformly filled is impractical.
A further problem associated with grout capsules concerns the addition of a reactive catalyst to the capsule or cartridge. Generally the cartridges are supplied in a powdery form contained within a permeable sheath formed of a material such as paper. Where the catalyst is water, the usual system for bringing the powder into contact with the water catalyst is to immerse the capsules into ground water in the mine. Contaminants in the ground water may result in the material within the capsule not setting effectively.
This arrangement is also unsatisfactory in that as soon as the capsules are placed in the water, the chemicals in the capsule begin to react. Although capsules can be selected with different hardening times, the system is inherently difficult to control. Premature hardening will clearly be unsatisfactory since hardened capsules cannot be inserted into the borehole. Capsules which have a long hardening time are unsuitable since there is an attendant time delay before the rockbolt which is to be grouted into position by the capsule can carry a load.
In practice it is found that a high percentage of capsules are wasted as a result of difficulties in insertion thereof into the borehole after the capsules have been mixed with their catalyst. Capsules are also wasted as a consequence of absorbing too great a quantity of catalyst after being simply dropped into a bath of catalyst, such as water. Over-watering of the capsules upsets the cement to water ratio, thereby weakening the capsule once it has hardened.